Amid talk of a special session of Parliament being convened sometime in September to pass the GST Bill, the Congress on Wednesday bluntly told the Narendra Modi government that the key reform measure could not be passed without its support, suggesting that its concerns needed to be taken on board.

The party also hit back at Finance Minister Arun Jaitley saying he had no moral authority to attack the Opposition on stalling the measure, given that Narendra Modi had “single-handedly sabotaged” it for three years when he was Gujarat Chief Minister.

“In politics, there is a thought and an after-thought,” party leader Jairam Ramesh told reporters, taking a dig at Jaitley who had accused Congress reservations to the GST in its present form as an “after-thought”.

“BJP, Narendra Modi and Yashwant Sinha (who was Chairman of the Parliamentary Standing Committee on Finance in the last Lok Sabha) are responsible for the delay in GST,” Ramesh said.

Ramesh said that as Union Minister he had gone to Gandhinagar in September 2012 and met Modi to garner his support for the Bill, but Modi had “single handedly sabotaged” it. “GST at that time came to be known as Gujarat Sabotage Tax,” he said taking a dig at Modi.

Dismissing suggestions that Congress was isolated on the GST issue, he said the Left parties and AIADMK and DMK were also opposed to the measure. Congress – which had initiated the GST Bill in 2006 – is strongly opposed to it in the present form and is insisting on three key amendments, including capping the tax at 18 per cent and removing the one per cent additional tax. Jaitley has ruled out incorporating these changes.

Government is keen on meeting the April 1, 2016 deadline for the implementation of the landmark tax system that would arguably increase the country’s GDP by one to 1.5 per cent.

After both Houses of Parliament clear the Constitutional amendment, half the states will also have to pass it.